The use of x-rays to form corresponding images comprises a well-understood area of endeavor. Generally speaking, an object exposed to a beam of photons from an x-ray source will block (or not) some portion of those photons as a function of its electron-density and its thickness. A detector array then detects where the photons have been attenuated to a corresponding greater or lesser degree and a corresponding image can be formed.
In such cases, the amount of radiation used can comprise a significant concern. On the one hand, higher radiation doses often contribute to superior image quality and increased detail resolution. On the other hand, lower radiation doses pose fewer safety issues, both to the object being inspected and the local environs. In some application settings enough information is available regarding the object to be inspected (such as information regarding the material comprising the object, the dimensions and geometry of the object, and so forth) to permit the selection of a particular radiation dose by a human operator that represents a useful compromise between these competing interests. Other application settings, however, are not amenable to such an approach. Another related concern is that some application settings are based upon a specific radiation safety design that allows a certain amount of average radiation to be used for imaging. By using lower doses for less attenuating portions of the object, a higher dose can be applied to more attenuating portions, thereby improving imaging quality.
Cargo inspection stations are an illustrative example in this regard. In many cases, a tractor and trailer to be inspected in this manner have unknown contents. In other cases, the contents may be generally known, but their relative locations within the vehicle may be unknown. In yet other cases, the contents as described of record may not in fact accord with the actual contents of the vehicle. Using some maximum level of radiation to account for such variations and uncertainties can permit the contents, regardless of their make-up, to be suitably imaged but this, in turn, presents the aforementioned traditional trade-off; corresponding safety issues can loom largely in such a case and ultimately discourage the use of such an approach.
Skilled artisans will appreciate that elements in the figures are illustrated for simplicity and clarity and have not necessarily been drawn to scale. For example, the dimensions and/or relative positioning of some of the elements in the figures may be exaggerated relative to other elements to help to improve understanding of various embodiments of the present invention. Also, common but well-understood elements that are useful or necessary in a commercially feasible embodiment are often not depicted in order to facilitate a less obstructed view of these various embodiments of the present invention. It will further be appreciated that certain actions and/or steps may be described or depicted in a particular order of occurrence while those skilled in the art will understand that such specificity with respect to sequence is not actually required. It will also be understood that the terms and expressions used herein have the ordinary technical meaning as is accorded to such terms and expressions by persons skilled in the technical field as set forth above except where different specific meanings have otherwise been set forth herein.